#define TIMER0 __vector_7
#define SIGNAL __attribute__ ((signal))

#define PORTB   (*(volatile unsigned char *)(0x38))
#define DDRB    (*(volatile unsigned char *)(0x37))
#define SREG    (*(volatile unsigned char *)(0x5f))
#define TCCR0   (*(volatile unsigned char *)(0x53))
#define TIMSK   (*(volatile unsigned char *)(0x59))

int counter = 0;

void TIMER0(void) SIGNAL;

void TIMER0(void)
{
    counter++;
    if (counter == 230)
    {
        PORTB = ~PORTB;
        counter = 0;
    }
}

int main(void) {
    TIMSK = TIMSK | 0x02;
    SREG  = SREG  | 0x80;
    TCCR0 = TCCR0 | 0x05;
    DDRB = 0xff;
    while(1) { }
    return 0;
}